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When Truck is Put in Reverse the Trailer Brakes Lock Up


I have a 1979 chevy shortbed truck, when I put the truck in reverse the breaks on the trailer are locked up. can you help with this problem the truck has a 6 pin plug.Thank you.


Expert Reply:

Are you certain that you have the 6-way connector, like part # PK12720 with the 6 round pins? Or do you have the 7-way connector like part # PK11893 that features 6 blade-type pins with one connector in the center? The two can sometimes be confused.

There are two possible reasons why the brakes are locking up on the trailer. If you have a surge or hydraulic coupler on the trailer, such as those typically found on boat trailers, the hydraulic brakes will lock up when the vehicle reverses unless the lock-out circuit on the coupler is wired to the trailer connector on the vehicle. How this is done will depend on the type of trailer connector you have.

If the trailer brakes are electric, and the trailer does not have a surge coupler, either the connector on the trailer or on the vehicle is wired incorrectly. If you look at the trailer wiring FAQ I have linked to, you can see that on the 7-way connector, if the circuit that is supposed to feed the center pin on the trailer connector is wired incorrectly, it can feed the brake output circuit on the trailer. This would cause the trailer brakes to actuate once the transmission is placed in reverse.

expert reply by:
Mike L

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